12 WINTER 2015 PHI KAPPA PHI FORUM
isotopic content of the layers and get a clue to
ocean temperature during the life of the animal. As we studied the
remains, we sought deviations from the patterns
of species and temperatures that dominate the
region today — and we
found them.

In a series of papers
starting 20 years ago, 8
my colleagues and I established a chronology
of El Niño frequencies
across the Holocene.

From the start of the
epoch until about 9,000
years ago, El Niño was
present but with an unknown frequency. From
about 9,000 to 6,000
years ago, El Niño was
absent or very rare. It returned about 5,800 years
ago, but until about 3,000
years ago, it was notably less frequent than today. El Niño frequency has varied over the last

3,000 years, but in general, it has been fairly
common, with three or more mega-events
during most centuries.

Much of archaeologyis about pattern recogni-tion: How does the dis-tribution of the materialremains that we excavatereflect human behavior inthe past? As an archaeol-ogist working on El Niño,I am particularly inter-ested in seeing whetherthe patterns we found inEl Niño’s behavior hadparallels in the history ofancient Peruvians. Thereare some fascinating cor-relations. When El Niñodisappeared early in theHolocene, human popula-tions on the coast slowlybegan to increase and toadopt agriculture, mostlycrops domesticated else-where — gourds, squashes, beans, varioustubers, and fruits. They began to live in smallvillages, but evidence for any social complexi-ty (hierarchies, people with power over others)is scant. When El Niño started again about5,800 years ago, human populations grewmore quickly and began to live in larger set-tlements that included increasingly large tem-ples requiring a great deal of organized laborto construct. Some sites have residential areasfor what appear to be different social classes.The size and number of these monumentalsites grew in the 3,000 years of infrequent ElNiños. It is tempting to think the early priestswe believe were in charge came to power bypromising to mitigate El Niño if the populacewould obey them and build temples, but wehave no way to know. Correlations in time —the juxtaposition of parallel patterns — are in-triguing and suggestive, but they do not provecausation.

In any event, when El Niño became more
frequent, going from perhaps once a century to every one or two decades, everything
changed. The monumental sites were abandoned. The people didn’t disappear, but their
religious system seems to have collapsed. Did
they suffer a crisis of faith when the temples
no longer held El Niño at bay? Some centuries

Excavating El Niño flood deposits at the site of San José de Moro in the Jequetepeque Valley, northern Peru. The levels date before 400 AD and sho w how the floods constructed the landscape on which the site was later built.

Much ofarchaeology isabout patternrecognition: Howdoes the distributionof the materialremains that weexcavate reflecthuman behaviorin the past?